Interesting read for those involved in the "Hybrid Rant" discussions........
Most of the world's living species of python are found in Australasia. McDowell (1975) points out the dramatic speciation of the Pythonidae in Australasia as compared to the rest of the world where relatively few species are found; and that was before the status or existence of Liasis perthensis, Morelia (=Python) carinatus and Python oenpelliensis, was confirmed.
Python reticulatus and Python amethystinus appear to be very closely related but in the wild at least do not interbreed (they are found together on Ceram and Ambon (McDowall 1975)). Python timorensis is apparently intermediate between the two species and hence it may be assumed that the three above species arose from the same stock in recent geological history, from the Australasian region. The two sub-species of Python amethystinus, Python amethystinus amethystinus (of New Guinea and adjacent islands) and Python amethystinus kinghorni (of Australia) obviously arose in very recent times as a result of the separation of Australia and New Guinea by Torres Strait. It is almost certain that Python amethystinus invaded Australia from New Guinea. The origins of Python oenpelliensis described by Gow in 1977 are uncertain.
Liasis olivaceous and Liasis papuanis are very similar species whose speciation has occurred in recent geological times again as a result of rising sea levels separating Australia and New Guinea. Liasis mackloti (=fuscus) is also in this group of pythons although its evolutionary relationship with other species is unclear. This group of snakes, whose original centre of distribution could be either Australia or New Guinea are sufficiently distinct in external morphology from other Australasian Pythons to warrant them being placed in a group of their own (Genus Lisalia), although the recent breeding of Water Python and Carpet Python, Scrub Python and Carpet Python (at the Royal Melbourne Zoo) indicates that the three genera are only of recent origin (geologically speaking).
The drying up of the Australian continent, particularly over the last million years, has certainly led to a rapid speciation and sub-speciation in Australian Pythons. Morelia spilotes (all forms) has evolved primarily for the Australian climate (mainly dry), whilst Morelia (=Chondropython) viridis could be described as New Guinea's evolutionary counterpart to the Australian Carpet Snake. 'Genetic conservatism' would probably have been the reason for the prevention of the evolution of a green 'Morelia' in Australia where gene flow in and out of Rainforests was high due to a shortage of rainforest habitat. In New Guinea no such problem would have existed where virtually the whole island was closed forest. In recent geological times when sea levels permitted movement across Torres Strait Morelia (=Chondropython) viridis would have invaded Australia whilst Morelia spilotes would have invaded New Guinea. Neither species has been able to disperse widely in their newly invaded islands. Within Australia an evolutionary offshoot of the Morelia spilotes line gave rise to Morelia (=Python) carinatus. No doubt some of the isolated geographical races of Morelia spilotes will eventually give rise to new species in their own right,(e.g. Morelia (=Python) spilotes imbricatus).
Liasis (=Python) boeleni, according to MeDowall represents an evolutionary intermediate between Python amethystinus and Morelia spilotes. The origins of Liasis boeleni are in doubt although presumably in the New Guinea area. Theoretically (if McDowall's conclusions are correct) it should be possible to interbreed in captive controlled conditions Liasis boeleni with Morelia spilotes or Python amethystinus. How Liasis boeleni is evolutionarily linked to other 'Liasis' is not certain.
Finally we are left with the remainder of the genus Liasis. which was presumably split between Australia and New Guinea several million years ago. Liasis childreni and Liasis perthensis speciated in Australia, and Liasis albertisi and Liasis (=Bothrochilus) boa arose in New Guinea. Liasis boa which appears intermediate to Liasis childreni (and L.perthensis) and Liasis albertsi would not constitute a stock linking those species directly, although in the distant past all four species presumably had the same ancestor.